In semiconductor device manufacturing, plasma etching using a processing gas may be carried out in fine processing of a thin film formed on a workpiece. The thin film may, for example, be a silicon compound film such as a silicon nitride film or a silicon oxide film, an organic film having carbon as a main component that is formed from amorphous carbon, a photoresist composition, or the like, or an inorganic film having an inorganic substance as a main component that is formed from a polycrystalline silicon film, amorphous silicon, or the like. In a case in which one or more specific thin films from among these thin films are etching processing targets and other films are non-processing targets, it is necessary to selectively etch processing targets relative to non-processing targets formed on the same workpiece. In other words, it is necessary to increase the selectivity in etching. Moreover, in recent years, there has been demand for further reduction of environmental impact in semiconductor device manufacturing.
For this reason, plasma etching methods for selectively etching a silicon oxide film on a substrate (workpiece) have been proposed (for example, refer to PTL 1). PTL 1 discloses a plasma etching method that uses a plasma etching gas containing a C3 or C4 fluorocarbon that includes a bromine atom and at least one unsaturated bond and/or ether bond. This plasma etching method enables excellent etching selectivity of a silicon oxide film using a plasma etching gas that has a short atmospheric lifetime and comparatively low environmental impact.